It is well known that LED illumination has non-substitutable advantages such as energy saving, ultra low power consumption, an almost 100% electro-optical power conversion, 80% or higher energy saving compared with traditional light sources at the same luminous efficiency, and a relatively long service life. Considering the advantages mentioned above, LEDs are more and more used as light sources, for example, LED retrofit lamps appearing in the market in a great number. Such LED retrofit lamps possess a contour of traditional light sources, an incandescent lamp or a lamp tube for instance, and can thus be better adapted to an existing lighting system as light source.
In an existing technical solution of retrofit lamps for replacing traditional lamp tubes, the retrofit lamp has a lamp tube made of a transparent plastic, an LED light engine as light source is arranged inside said lamp tube, an additional holding structure is hereby usually required to fix the LED light engine, and said holding structure arranges the LED light engine on end caps closing two open ends of the lamp tube. In another existing technical solution, the retrofit lamp, viewed from a cross section thereof, includes two parts, viz. a lamp cover of a transparent plastic and a heat sink that is assembled together with the lamp cover and used for an LED light engine, wherein the heat sink and the transparent lamp cover are assembled to form a cylindrical structure. Hereby, both the heat sink and the transparent lamp cover require a specifically configured mounting structure, so that good leak tightness is assured, while the two are reliably fixed together. However, the above solutions have certain obvious disadvantages, viz. the holding structure has to be specifically configured, which increases the cost of the retrofit lamp resulting in complexity and difficulty of assembly. In addition, a lamp tube made of plastics has relatively bad flexural behavior, and might have undesired bend in case of a relatively long lamp tube. In order to solve said problem, the heat sink has to be configured to be relatively heavy, which increases the cost of the retrofit lamp. Moreover, a plastic lamp cover has relatively bad optical performance, and complex configurations have to be performed on the plastic lamp cover to obtain desired light distribution performance, which further increases the cost of the retrofit lamp.